Cameras, and other imaging devices, with the capability to provide increasingly high dynamic range images, are becoming more widely available. Such HDR images are able to capture a wider range of luminosity or brightness than is possible with more traditional imaging devices and techniques. This can be useful when the subject matter of the photograph contains both extremely bright and extremely dark regions, such as, for example, a mixture of sunlit areas and shadowed areas. HDR imaging is sometimes accomplished by capturing multiple images of the same scene, each taken at narrow but varying exposure levels, and combining them into a composite image. HDR images may also be obtained with sensors that have greater dynamic range, and which can generate pixel values with an increased number of bits to represent that entire range, without losing detail through truncation of least significant bits.
Currently, however, most conventional display devices have much more limited dynamic range (e.g., low dynamic range or LDR), and are unable to reproduce such HDR images in a visually acceptable format. Attempts to display an HDR image on a standard or conventional LDR display typically result in regions of the image that are either washed out or blacked out, or both, with a resulting loss of image detail. Existing solutions to this problem attempt to reduce image contrast through either global or local tone (e.g., luminosity and/or color) mapping operations. Global operators apply the same mapping function to each image pixel and provide global contrast reduction, but typically suffer from loss of detail in the dark and bright areas of the image. Local operators, on the other hand, are better at preserving local image features such as details in bright and dark areas, but generally suffer from low global contrast and may introduce image artifacts such as halo effects. Additionally, local tone mapping operators are more computationally intensive and are generally not suitable for real-time applications.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art.